1. Field of the Invention
This invention relates to an electrophotographic copying apparatus of the image transfer type in which illumination light is applied to a predetermined width area of the side edge portion of a movable electrophotographic photosensitive medium to form a light portion potential on this area and prevent developer from adhering to such area.
2. Description of the Prior Art
For example, in a copying apparatus wherein a visible image of an original is formed on a movable electrophotographic photosensitive medium and the visible image is transferred to transfer paper, the transfer paper having the visible image transferred thereto must be separated from the photosensitive medium. The method of forcibly separating the transfer paper from the photosensitive medium by causing the side edge portion of the transfer paper to engage belt-like means, pawl-like means or the like is known. This separator means in the form of a belt, a pawl or the like is caused to bear against or be in proximity to the side edge portion of the photosensitive medium. If developer adheres to a predetermined width area of the side edge portion of the photosensitive medium against which or to which the separator means bears or is in proximity, the separator means will be contaminated by the developer, because where the separator means bears against the photosensitive medium, it scrapes the developer from the photosensitive medium and, even where the separator is spaced apart from the photosensitive medium, when a predetermined width area of the side edge portion of the transfer medium engages the separator means, the developer transferred to that portion of the transfer medium adheres to the separator means. In any case, if the separator means is thus contaminated by the developer, unsatisfactory separation of the transfer medium from the photosensitive medium will occur and there will also occur inconveniences that the image is disturbed and that the transfer medium is contaminated. For this reason, it has heretofore been practised to impart supplemental exposure light to that portion of the photosensitive medium against which or to which the separator means bears or is in proximity, to thereby provide a sufficient light portion potential to that portion and prevent adherence of the developer from occurring during development. Heretofore, the device as shown in FIG. 1 of the accompanying drawings has been common as a device for imparting such supplemental exposure light.
In FIG. 1, reference character 1 designates a drum having an electrophotographic photosensitive medium on the peripheral surface thereof and rotatable about the axis X thereof. The effective image forming area 3 of the photosensitive medium (that area of the photosensitive medium on which the image of an original to be transferred is formed) is slit-exposed to the original image through a lens 2. Designated by 4 is the portion against which the aforementioned separator means 12 bears. This portion 4 is a side edge portion of the photosensitive medium with respect to the direction of the bus bar thereof, and it is a small width area adjacent to the effective image forming area 3. Supplemental exposure light is imparted to this portion 4 from a lamp 5 disposed within a light-shielding housing 6 having a slit opening in the lower portion thereof and the image of the original is not formed on this portion. However, such a device has the following disadvantages.
(1) Since the light source 5 for supplemental exposure is near the photosensitive drum, part of the light emitted through the opening of the housing 6 becomes so-called stray light and comes round to the effective image area 3, also.
(2) The opening of the housing 6 cannot be sufficiently proximate to the photosensitive drum. Therefore, supplemental exposure for clarifying the boundary between the areas 3 and 4 is difficult.
(3) The light source 5 is specially necessary for supplemental exposure.